Two-coil linear motion device



June 10, 1969 TWOCOIL LINEAR MOTION DEVICE Filed Sept. 1. 1967 Sheet I ,orz

FIGJA r. F. HURSEN 3,449,603

June 10, 1969 T. F. HURSEN 3,449,603

TWO'COIIJ LTNEAR MOTION DEVICE Filed Sept. 1, 1967 Sheet 2 of 2 wumsssgs: Th il wnamoa H=&,V%, omos ursen United States Patent 3,449,603 TWO-COIL LINEAR MOTION DEVICE Thomas F. Hursen, Monroeville, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pin, a corporation of Pennsylvania Filed Sept. 1, 1967, Ser. No. 664,977 Int. Cl. H02k 41/02 US. Cl. 310-12 9 Claims ABSTRACT OF THE DISCLOSURE The structure and operation of a linear motion device of the magnetic jack type are simplified by utilizing only two solenoid operating coils and gripper assemblies instead of three or more solenoids to produce bi-directional linear motion of a drive rod, or other element, in stepby-step manner.

Background of the invention This invention relates, generally, to linear motion devices and, more particularly, to devices of the magnetic jack type having gripper assemblies for rectilinearly moving a drive rod, or other element, in a step-by-step manner.

Prior linear motion devices of the magnetic jack type have required at least three solenoid operating coils to move a drive rod, or other element, linearly in opposite directions. The normal operation of a three-coil magnetic jack mechanism involves the sequential energization of the operating coils by means of a preset cam switch arrangement. By energizing each of the three operating coils in a proper sequence, the magnetic field generated by each coil acts through a pressure housing to produce movement in magnetic pole pieces inside the pressure housing. The movement of these pole pieces produces motion in latch sets or gripper assemblies which are used to engage, disengage or move a grooved drive rod up or down.

An object of this invention is to provide a simple and reliable linear motion device of the magnetic jack type that requires only two solenoid operating coils.

A further object of the invention is to utilize duplicate 'parts in the coil assemblies, thereby reducing the manu facturing cost.

Another object of the invention is to provide a magnetic jack mechanism that can apply force to a drive rod in either of two opposite directions.

Other objects of the invention will be explained fully hereinafter or will be apparent to those skilled in the art.

Summary 0 the invention In accordance with the present invention only two solenoid operating coils, designated as coil 1 and coil 2, are utilized to provide step-by-step linear motion of a linearly movable element or drive rod. Coil 1 can cause the drive rod either to move up or remain stationary. Coil 2 can cause the drive rod either to move down or remain stationary. When coil 1 is energized at a reduced voltage, its assocaited gripper assembly engages the drive rod to hold it stationary, and when this coil is energized at a higher voltage the drive rod is moved up one step. When coil 2 is energized at a reduced voltage its gripper assembly engages the drive rod to hold it stationary and when this coil is energized at a higher voltage the drive rod is moved down one step. Springs of different strengths are utilized in the gripper assemblies to cooperate with the coils in obtaining the desired sequence of operation.

Brief description 0 the drawing For a better understanding of the nature and objects of the invention, reference may be had to the following 3,449,603 Patented June 10, 1969 Description of the preferred embodiment In the structure illustrated in the drawing, the gripper members of the linear motion device may be located in three relative positions with respect to a linear element or drive rod 16 which is moved by the gripper members.

One of the relative positions is designated the unlatched position wherein the gripper is not in position for engagement with the projections or teeth on the drive rod. A second relative position is designated the latched" position wherein the gripper is engaged with the drive rod and the gripper is subjected to the load or weight of the drive rod. The third relative position of the components is designated the coupled position wherein the gripper is located in its engaged position relative to the drive rod, but the gripper is not subjected to the load created thereby. That is, a clearance exists between the teeth of the drive rod and the outward tip of the gripper arm or arms of the gripper assembly. A difference between the latched position and the coupled position of the gripper exists not with respect to the radial position of the gripper arms, but by virtue of ditferent axial positions of the drive rod relative to the gripper arms. In the latched position, the drive rod is in an axial position wherein the gripper is subjected to the load of the rod. In the coupled position, the drive rod is in an axial position wherein the gripper is not subjected to the load of the rod.

Referring to the drawing, the linear motion device shown therein may be generally of the type described in Patent No. 3,158,766, issued Nov. 24, 1964 to E. Frisch and assigned to the Westinghouse Electric Corporation. The device has a tubular outer housing 10 formed of nonmagnetic material, or magnetic material with nonmagnetic inserts of a thickness capable of withstanding a relatively high internal pressure. The housing 10 is provided with two annular solenoid coils 1 and 2 mounted on the outer surface thereof in an axially spaced relationship. Each solenoid coil includes a winding 11 and a support structure 12 which forms a flux path for magnetic flux generated by the winding 11. The two solenoid coils are maintained in spaced relation on the housing 10 by spacing sleeves 13 and 14. The lower end of the housing 10 is threated into a lower housing member 15 which may be secured in a suitable manner to a pressurized system with which the linear motion device is utilized. The lower end of the spacing sleeve 14 rests on the housing 15. The upper end of the housing 10 is desirably closed off by a cover (not shown) which may be secured to.the housing 10 by suitable means to ensure hermetic integrity of the housing.

A linearly movable element or drive rod 16 is disposed inside the housing 10. The drive rod 16 has a plurality of axial-1y spaced projections or teeth 17 thereon. In order to move the drive rod 16 linearly or axially, two gripper assemblies 21 and 22 are mounted inside the housing 10 around the drive rod 16 and axially spaced relative to the rod. The grip-per assembly 21 is associated with the solenoid coil 1 and the gripper assembly 22 is associated with the solenoid coil 2. By energizing the solenoid coils in a manner to be described hereinafter, the drive rod 16 can be moved either up or down in a stepby-step manner, or caused to remain stationary.

The gripper assembly 22 comprises a fixed annular pole piece 23, a movable annular pole piece 24, three circumferentiallly spaced gripper arms 25 each one of which is pivotally mounted in a recess 26 in the pole piece 24 by means of a pin 27, a movable pole piece 28 which is pivotally attached to the arms 25 by links 29 and pins 31 and 32, a compression spring 33 disposed between a shoulder 34 on the pole piece 24 and a nonmagnetic shim 35 on the pole piece 28, and a compression spring 36 disposed between a shoulder 37 on the pole piece 24 and a nonmagnetic shim 38 on the pole piece 23. Each gripper arm 25 has an inwardly extending tip 39 of a size to fit between the teeth or projection 17 on the drive rod 16 with an axial clearance therebetween.

The fixed pole piece 23 has a projection 41 which is clamped between a shoulder 42 on the housing and a locking ring 43 threaded into the lower end of the housing 10. The lower end of a spacing sleeve 44 is threadedly attached to the fixed pole piece 23. The sleeve 44 has slots 45 therein through which the arms project to engage the drive rod 16.

Likewise, the gripper assembly 21 comprises a fixed annular pole piece 46 threadedly attached to the spacing sleeve 44, a movable annular pole piece 47, three circumferentially spaced gripper arms 48 pivotally mounted on a movable support member 49 by means of pins 51, a movable annular pole piece 52 pivotally attached to the gripper arms 48 by links 53 and pins 54 and 55, a compression spring 56 disposed between a shoulder 57 on the pole piece 47 and a nonmagnetic shim 58 on the pole piece 52, and a compression spring 59 disposed between a shoulder 61 on the pole piece 47 and a nonmagnetic shim 62 on the pole piece 46. The support member 49 is disposed in a recess 63 in the pole piece 47 and a compression spring 64 is disposed in the recess between the member 49 and the pole piece 47. The pole piece 47 has an inwardly extending projection 65 thereon for engaging a shoulder 66 on the support member 49. The spring 56 biases the pole piece 52 towards a shoulder 67 on the spacing sleeve 44. The spring 59 biases the pole piece 47 towards a stop ring 68 fixedly secured to the sleeve 44. The sleeve 44 has slots 69 therein through which the gripper arms 48 project to engage the drive rod 16.

In the gripper assembly 22, the spring 36 biases the pole piece 24 towards a stop ring 71 fixedly secured to the spacing sleeve 44. Likewise, the spring 33 biases the pole piece 28 towards a shoulder 72 on the spacing sleeve 44. The spring 36 is stronger than the spring 33. In the gripper assembly 21, the spring 59 is stronger than the spring 56. The pole pieces 28 and 52 are of identical construction. Likewise, the gripper fingers 25 and 48 are of identical construction, thereby reducing the cost of manufacturing them. These parts are reversed in position in the two gripper assemblies. The nonmagnetic shim 62 is thicker than the nonmagnetic shim 58 in FIG. 1A. Likewise, the nonmagnetic shim 38 is thicker than the nonmagnetic shim in FIG. 1B for a purpose explained hereinafter.

In order to raise the element or drive rod 16 one step, the winding 11 of solenoid will is first energized at a reduced voltage of enough magnitude to induce a magnetic force between pole pieces 52 and 47 that can overcome the weight of pole piece 52 and the force of spring 56, thereby first actuating the gripper arms 48 to the coupled position in which the tips 73 of the arms are in a groove between two teeth 17 of the drive rod yet axially spaced therefrom. As the pole piece 52 continues to move upwardly, the shim 58 engages the bottom end of the support member 49 to raise arms 48 to the latched position in which the tips 73 engage a tooth 17, thereby carrying the weight of the drive rod 16 as shown in FIG. 1A. The load transfer spring 64 prevents the support member 49 and arms 48 from moving upwardly while the arms 48 are being actuated about the pivot pins 51 by the links 53 during the first part of the upward travel of the pole piece 52. It is important that the final magnetic force after the pole pieces 52 and 47 are closed be low enough that the weight of the drive rod 16 and the pole pieces 52 and 47 and the force of the spring 59 is not exceeded. If this latter condition is properly achieved, the arms 48 will engage the drive rod, as shown, and then remain stationary.

To produce a lifting motion, winding 11 of solenoid coil 1 is further energized with its full voltage, thus increasing the total magnetomoti've force to a level that produces a magnetic lift force equal to approximately twice the drive line weight, including the force of the spring 59 which is compressed when the gap between pole pieces 46 and 47 is closed, thereby causing the projection 65 to engage the shoulder 66 to raise the support member 49, the arms 48 and the drive rod 16. A doubling of the force is required in order to achieve a reasonable speed of motion. In this manner the drive rod 16 is raised one step or the distance between two teeth 17 on the drive rod.

Next, the winding 11 of solenoid coil 2 is energized with a reduced voltage such that pole piece 28 moves downward against the force of spring 33 to close the gap between pole piece 28 and pole piece 24 in order to actuate the arms 25 into an appropriate groove in the drive rod 16. The arms 25 are now in the coupled position in which there is about inch axial clearance between the upper side of each tip 38 and the lower side of a tooth 17. Now that the lower gripper arms are in a position to grasp the drive rod, the winding 11 of solenoid coil 1 is completely de-energized. Since the net magnetic retentive force between the pole piece 47 and the stationary pole piece 46 is less than the magnetic lfOICG between the pole pieces 52 and 47 for any level of total magnetic flux (by reason of the relative area, shim size, pole weight, and spring force), the former gap begins to open first. This motion lowers the drive rod 16 until the clearance between the gripper arms 25 and the tooth 17 closes and the weight of the drive line is effectively transferred from gripper arms 48 to arms 25 without :any sliding motion under load. The arms 25 are now in the latched position.

As the flux around solenoid coil 1 continues to decay, the gap between pole pieces 52 and 47 also starts to open, and the two operating gaps continue opening together. This simultaneous action moves the tips 73 down against the opposite side of the rod groove after the load transfer has occured with the result that the arms 48 effectively cam out against the bottom of the groove. This motion occurs under a light load over a portion of the tooth and will not compromise either the operation of the mechanism or the life of the moving parts. This has been demonstrated by a life test in excess of 1x10 cycles on a three coil linear motion device. To continue step-by-step movement in the upward direction, the whole cycle as described above is repeated.

Downward motion of the drive rod 16 is accomplished in a similar manner except that solenoid coil 2 is utilized to permit a lowering of the drive rod. The arrangement shown in FIG. 1B puts the gripper arms in general compression. This is done in order to use identical operating parts in the construction of each of the solenoid coil asemblies for economic reasons. The lower gripper arms could be constructed to take the load in tension; however, this would increase the cost of manufacture. Although the mechanical parts and the solenoid coils can Ewe identical, the springs are not, as explained hereinbeore.

With the linear motion device in the position shown in FIGS. 1A1B, downward motion is obtained by energizing the winding 11 of the solenoid coil 2 at a reduced voltage to close the gap between pole pieces 28 and 24 against the force of spring 33, thereby actuating the gripper arms 25 to the coupled position. Next, the winding 11 of solenoid coil 1 is de-energized, thereby permitting the drive rod 16 to drop the slight distance between shoulder 66 and projection 65 to cause the lower side of a tooth 17 to engage the tips 39 on the arms 25 which are now in the latched position. The weight of the drive rod is now supported by the spring 36. Further downward travel of pole piece 52 actuates arms 48 to the unlatched position. The winding 11 of solenoid coil 2 is next energized with a higher or full voltage to close the gap between pole pieces 23 and 24 against the force of spring 36 and lower the drive rod 16 one step. The winding 11 of solenoid coil 1 is then energized at a reduced voltage to actuate the gripper assembly 21 to the position shown in FIG. 1A which transfers the weight of the drive rod 16 from the gripper assembly 22 to the assembly 21 in the manner hereinbefore described. 'In order to lower the drive rod another step the foregoing cycle is repeated.

Since there are two air gaps in series with each magnetic circuit for the solenoid coils, it is necessary to increase the maximum MMF by about as compared with prior linear motion devices of the magnetic jack type in which each solenoid coil has only one air gap. Furthermore, it may be desirable to provide a current regulator in the energizing circuit for the windings of the solenoid coils in the event compensation for changes in the resistance of the windings with temperature changes is required. Suitable current regulators are well known in the art. Control means for controlling the sequential energization of the solenoid coils are also well known.

As explained hereinbefore, the nonmagnetic shims in the pole gaps for each solenoid coil are of a different thickness, and the pole areas at each working gap are different to adjust the forces at each pole gap at each time in the cycle of operation. Furthermore, in order to avoid an excessive force after the first working gap is closed, which is before the MMF is increased to its maximum value, a tapered contour is provided in the pole pieces 28 and 52. This is designated by the reference numeral 74 in the drawing. Spaced ridges 75 are provided around the outer periphery of the contour to act as guides for the pole pieces.

The tapered contour has the net efiect of producing a smaller increase in the magnetic force at the working gaps as the pole pieces close. As an example, consider the pole piece 52. As this pole piece moves toward the closed position, a reduction in magnetic resistance occurs locally at the working gap by reason of the following relationship:

where:

R is the magnetic resistance,

L is the length of the gap,

A is the working area, and

a is the permeability of the air gap.

This reduction in resistance produces an increase in the total flux, by the relationship MMF=ER, when the MMF is held constant. This increase in total flux produces an increase in the flux density B at the working gap, and thus an increase in the operating force that is proportional to B as follows:

Force:B A 72 The net result is an increasing magnetic force as the working gap closes. By using a tapered pole piece, the radial air gap between the tapered pole piece and the coil housing increases as the working gap decreases. By selecting the correct taper, this increase in radial air gap can be used to partially offset the closing of the working air gap, thereby obtaining the desired amount of magnetic force.

From the foregoing description it is apparent that the invention provides a simple and reliable linear motion device which can drive a linearly movable element in either of two opposite directions since the device can produce a driving force in either direction. Therefore, the device is not limited to vertically moving elements, but can be utilized to drive horizontally moving elements. The present device requires only two solenoid operating coils as compared with at least three required by prior devices of the same general type.

Since numerous changes may be made in the abovedescribed construction, and dilferent embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the subject matter contained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustive to the element, a first solenoid coil for operating one gripper assembly to engage the projections and hold the element stationary when energized at a reduced voltage and move the element linearly in one direction when energized at a higher voltage, and a second solenoid coil for operating the other gripper assembly to engage the projections and hold the element stationary when energized at a reduced voltage and move the element linearly in the opposite direction when energized at a higher voltage.

2. The linear motion device defined in claim 1 wherein each gripper assembly includes resilient means cooperating with the solenoid coil for that assembly in obtaining the desired sequence of operation of the assembly.

3. The linear motion device defined in claim 2 wherein the resilient means comprises at least two springs of different strengths.

4. The linear motion device defined in claim 3 wherein the springs in each gripper assembly jointly oppose the magnetic force produced by the solenoid coil for that assembly.

5. The linear motion device defined in claim 1 wherein each gripper assembly includes at least two movable magnetic pole pieces and a pivotally mounted gripper arm, one of said pole pieces being operated to actuate the arm to engage the projections when its associated solenoid coil is energized at a reduced voltage and the other pole piece being operated to move the element linearly when the associated coil is energized at a higher voltage.

6. The linear motion device defined in claim 5 wherein one of the magnetic pole pieces of each gripper assembly the corresponding members of the other gripper assembly.

8. The linear motion device defined in claim 1 wherein one of the gripper assemblies includes two movable magnetic pole pieces, a movable support member, a gripper arm pivotally mounted on the support member, pivotal means connecting one of the pole pieces to the gripper arm to actuate the arm into engagement with the element, and a projection on the other pole piece engaging the support member to move the arm and the element linearly.

9. The linear motion device defined in claim 8 wherein the pole piece which is pivotally connected to the gripper arm engages the support member to move it, and including resilient means opposing said movement of the support member.

References Cited UNITED STATES PATENTS 3,050,943 9/1962 Thorel et al. 310-12 XR 3,132,290 5/1964 Kumpf 3l7--123 3,122,027 2/1964 Frisch et al 31012 XR 3,158,766 11/1964 Frisch 3 l0'14 3,299,302 1/1967 Frisch 310-12 MILTON O. HIRSHFIELD, Primary Examiner.

B. A. REYNOLDS, Assistant Examiner.

US. Cl. X.R. 31014, 15 

